The objectives of this research project are to investigate the factors which control intestinal transport of calcium and the mechanism whereby these factors effect the calcium transport process. Specifically these investigations will be directed to the identification and characterization of the action of parathyroid hormone, vitamin C, and glucocorticoids on the intestinal transport of calcium and the examination of the role of these factors in the physiologic control of intestinal calcium absorption. Studies of the mechanism of parathyroid hormone action will be directed to the characterization of the influence of this hormone on a Na, Ca-dependent phosphatase isolated from the basal-lateral membranes of the mucosal cell. The influence of vitamin D on the cellular metabolism of the intestine and muscle will be investigated as well as the influence of glucocorticoids on the cellular response to vitamin D and its metabolites.